In a compressor refrigeration system, a certain amount of the heat energy that is developed at the compressor goes into heating the compressor itself and the oil by which the compressor is lubricated. To cool the oil sufficiently to maintain its lubricating qualities, and also to enable it to effect cooling of the compressor body, the compressor lubricating oil may be circulated through an oil cooler that is external to the compressor and in which the oil is passed in indirect heat exchange relationship with a cooling medium. In large refrigeration systems it has heretofore been conventional to use water as the cooling medium for the oil cooler. In many cases the circulation flow for such cooling water was arranged to include the compressor itself, and particularly its cylinder body, which was provided with a water jacket for the purpose.
Such water cooling of the compressor and its oil supply required a special circuit comprising a source of cooling water and provision for satisfactory disposition of the heated water as well as the necessary ducting and pump. Of course it was also necessary to provide the compressor body with a water jacket that increased the cost and complexity of the compressor. The present invention starts from the recognition that there is an inherent inefficiency in providing special facilities for cooling the compressor and its lubricating oil when there is already present in the refrigeration system a condenser that is intended for rejecting heat energy developed at the compressor.
From time to time others have recognized the anomaly in providing two different facilities for performing what is essentially one and the same function--heat rejection--but heretofore there has been no satisfactory proposal for an arrangement that would rationalize such refrigeration systems by causing all heat that must be abstracted from the compressor and its lubricating oil to be given off at the condenser.
U.S. Pat. No. 3,710,590, to Kocher, discloses a refrigeration system in which lubricating oil for a rotary screw compressor is cooled by indirect heat exchange with refrigerant drawn from the high pressure receiver by means of a pump. According to that patent, the refrigerant used for oil cooling, after being passed through the oil cooler, is sent through a desuperheating coil in an oil separator that is downstream from the compressor; and it is then directed back to the condenser through a duct separate from the duct that carries the compressed refrigerant. This arrangement takes care of cooling the lubricating oil for the compressor, but it does not provide for carrying off excess heat from the compressor itself. Furthermore, it fails to take advantage of a possibility that becomes apparent in the light of the present invention, namely, the employment of the refrigerant that has been passed through the oil cooler to increase the effectiveness of the oil separator.
U.S. Pat. No. 3,874,192, to Kato, discloses a refrigeration system wherein a certain amount of liquid refrigerant, taken from the high pressure receiver, is injected by means of a venturi-type atomizer into the stream of compressed refrigerant flowing from a screw compressor to an oil separator. The atomized liquid refrigerant is said to cool the oil that is entrained in the compressed refrigerant to a temperature of about 45.degree. C. and is said to cool the gas component of the compressed refrigerant "to a temperature in the vicinity of the condensation temperature of the condenser, that is, 30.degree. C. to 35.degree. C." This arrangement effects desuperheating of the compressed refrigerant at the same time that it improves the effectiveness of the oil separator by reason of the condensation of a certain amount of the entrained oil in the stream of compressed refrigerant; and the oil that is returned to the compressor from the oil separator may have a certain amount of effectiveness in cooling the compressor. However, as with the system proposed by Kocher, there is no provision for direct cooling of the compressor itself by means of refrigerant.
U.S. Pat. No. 4,062,199, to Kasahara et al, discloses an arrangement wherein oil that is separated at an oil separator from compressed refrigerant issuing from a screw compressor is passed through an oil cooler before being returned to the screw compressor. In one of the embodiments disclosed in that patent, the oil cooler is cooled by liquid refrigerant drawn from a high pressure receiver. The refrigerant that has been passed through the oil cooler is conducted through a supercooler, in indirect heat exchange with refrigerant that is flowing from the receiver to the evaporator, and then, as a gas at low temperature and intermediate pressure, it is injected into the compressor at an intermediate-pressure zone thereof. This arrangement employs compressed refrigerant for cooling of the compressor and its lubricating oil, thus eliminating the need for a cooling water circuit, but some portion of the capacity of the compressor has to be sacrificed to provide for such oil and compressor cooling.
Other arrangements have been proposed for employing compressed and cooled refrigerant as a medium for cooling the compressor and/or its lubricating oil, but in all such systems heretofore proposed the refrigerant used for that purpose has been returned to the low-pressure side of the compressor (or, as in Kasahara et al, to an intermediate pressure portion of the compressor) so that the compressor has had to recompress such refrigerant at the sacrifice of some of its capacity for compressing refrigerant for the refrigeration system proper. Furthermore, when such refrigerant was returned to the compressor inlet, it cooled only the portion of the compressor body that tended to be coolest anyway, and in being compressed along with the rest of the refrigerant fed into the compressor, it could not remove heat from the hottest parts of the compressor body. Thus prior compressor cooling expedients of this type brought about no real and substantial improvement in the capital cost of equipment needed for providing a given refrigeration capacity, and usually afforded no material improvement in the efficiency of the refrigeration system as a whole.